Exhaust gas heat exchanger

ABSTRACT

An exhaust gas heat exchanger comprising an external shell ( 20 ) extending between two tube plates ( 30, 31 ) and defining a coolant chamber; internal tubes ( 38 ) forming exhaust gas passages which extend between the tube plates ( 30, 31 ); an exhaust gas manifold divided by a baffle plate ( 29 ) into first and second chambers (26, 28) with an exhaust gas inlet ( 25 ) and outlet ( 27 ) respectively. The baffle plate ( 29 ) is provided with a valve ( 51 ) which can be operated between an open position, which exhaust gas flows along the cooling tubes ( 38 ), and a closed position, in which exhaust gas is diverted directly from the first chamber ( 26 ) to the second chamber ( 28 ).

FIELD OF THE INVENTION

This invention relates to an exhaust gas heat exchanger, and relatesmore particularly but not exclusively to an exhaust gas cooler forreducing the temperature of exhaust gases from internal combustionengines.

BACKGROUND OF THE INVENTION

FIGS. 1 a to 1 c of the accompanying drawings show a known exhaust gascooler. This prior art cooler comprises a circular shell 1 fitted withtapered ends 2 which serve as an exhaust gas entry orifice 3 and anexhaust gas exit orifice 4. The orifices 3 & 4 are provided with flangeplates 10 for connection to exhaust pipes (not shown). The ends of theshell 1 are sealed by circular tube plates 5 which define a coolantchamber inside the shell 1. Each tube plate 5 has a number of circularholes 6 arranged through it. The holes 6 in each tube plate 5 areconnected by a number of small-diameter tubes 7 which are sealed at oneend to the first tube plate 5 and at the other end to the second tubeplate 5. Exhaust gases flow into the entry orifice 3, along the insideof the small-diameter tubes 7 and out of the exit orifice 4. Theexterior of the shell 1 is provided with an entry nozzle 8 and an exitnozzle 9 which respectively supply coolant liquid to and drain coolantliquid from the coolant chamber within the shell 1.

Prior art exhaust gas coolers (such as that shown in FIGS. 1 a-1 c) arebulky and do not fit easily within the frequently cramped layout of theengine compartment of a road vehicle. The possible positions to fit anexhaust gas cooler within an engine compartment are limited by the factthat the exhaust gases flow into the cooler at one end and flow out atthe other end. At certain times, particularly during engine start-up, itis necessary to stop the exhaust gases being cooled. The prior artexhaust gas coolers therefore require special valve and bypass tubearrangements so that exhaust gases can be diverted around the exhaustgas cooler when cooling is not required.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an exhaust gas heatexchanger capable of functioning as a bypassable exhaust gas coolerwhich does not require separate means, such as a bypass pipe, to enableexhaust gas flow to bypass the cooler.

According to the present invention there is provided an exhaust gas heatexchanger of the shell and tube type, said heat exchanger comprising ashell having a hollow interior between opposite ends, an exhaust gasmanifold secured to one end of the shell, and thermally conductive tubemeans extending through the interior of the shell from said one end ofthe shell, the exhaust gas manifold comprising first and second exhaustgas chambers which are mutually adjacent, each of said exhaust gaschambers comprising a respective exhaust gas inlet and an exhaust gasoutlet, said tube means providing an exhaust gas flow path between theexhaust gas outlet of said first exhaust gas chamber and the exhaust gasinlet of said second exhaust gas chamber, said heat exchanger beingcharacterised by valve means providing a gas flow path directly betweensaid first and second exhaust gas chambers when said valve means isopen, said valve means substantially closing a direct gas flow pathbetween said first and second exhaust gas chambers when said valve meansis closed, whereby when a source of flowing exhaust gas is coupled tothe exhaust gas inlet of said first exhaust gas chamber and said valvemeans is closed, exhaust gas is constrained to flow from the exhaust gasinlet of said first exhaust gas chamber to the adjacent exhaust gasoutlet of said second exhaust gas chamber by way of said thermallyconductive tube means to exchange heat with fluid in the interior of theshell and surrounding said tube means, whereas when said valve means isopen, exhaust gas is allowed to flow from the exhaust gas inlet of saidfirst exhaust gas chamber directly to the adjacent exhaust gas outlet ofsaid second exhaust gas chamber and so bypass said tube means.

Said shell may be generally tubular between said opposite ends, and maycomprise a fluid inlet and a fluid outlet permitting the flow of fluidfrom said fluid inlet to said fluid outlet by way of the interior of theshell surrounding the thermally conductive tube means.

Said thermally conductive tube means may comprise a plurality of metaltubes each extending through said one end of the shell with a firstsub-set of said plurality of tubes extending from the exhaust gas inletof said first exhaust gas chamber through said other end of the shelland into a further exhaust gas chamber secured to said other end of theshell, and a second sub-set of said tubes extending from said furtherexhaust gas chamber through said other end of the shell to the exhaustgas inlet of said second exhaust gas chamber. Said further exhaust gaschamber may be defined by said other end of the shell together with adomed member secured to the shell around said other end.

Alternatively, the thermally conductive tube means may comprise aplurality of metal tubes each extending through said one end of theshell between the exhaust gas outlet of said first exhaust gas chamberand the exhaust gas inlet of said second exhaust gas chamber, with thetubes being U-shaped or any other suitable shape.

Said first and second exhaust gas chambers are preferably mutuallycontiguous on either side of a common internal wall of the manifold,said valve means being mounted in said common internal wall of themanifold. Said valve means may be a rotary valve mounted for rotationabout a rotation axis lying substantially in said common internal wallof the manifold.

The heat exchanger may be such that when said valve means is open toallow exhaust gas to flow from the exhaust gas inlet of said firstexhaust gas chamber directly to the exhaust gas outlet of said secondexhaust gas chamber, the valve means simultaneously closes either theexhaust gas outlet of said first exhaust gas chamber or the exhaust gasinlet of said second exhaust gas chamber, or said valve meanssimultaneously closes both the exhaust gas outlet of said first exhaustgas chamber and the exhaust gas inlet of said second exhaust gaschamber.

The exhaust gas heat exchanger is preferably made from stainless steel.The shell may be circular, oval or rectangular in cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference FIGS. 2-6 of the accompanying figures, wherein:

FIG. 2 is a partially cut away side elevation of a first embodiment ofexhaust gas cooler;

FIG. 3 is a sectional view on line III—III of the cooler of FIG. 2;

FIG. 4 is a perspective view of the end of the cooler of FIG. 2;

FIG. 5 is a perspective view from below of the cooler of FIG. 2; and

FIG. 6 is a partially cut away side elevation of one end of a secondembodiment of exhaust gas cooler.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIGS. 2 to 5, these show an exhaust gas cooler 19forming a first embodiment of exhaust gas heat exchanger in accordancewith the invention. The cooler 19 comprises an external cylindricalshell 20. An exhaust gas manifold 21 is secured to one end of the shell20, the manifold 21 being adapted to fit over the end of the shell 20and be fastened thereto by any suitable means, e.g. by welding. Themanifold 21 comprises a tapered conical portion 22 and a tubular portion23 whose diameter is less than the diameter of the cylindrical shell 20.At the other end of the shell 20 is a domed cover portion 24 alsoadapted to fit over the end of the shell 20 and be secured thereto bysuitable means, e.g. by welding. The volume between this end of theshell 20 and the domed cover 24 constitutes a further exhaust gaschamber 60 whose purpose will be subsequently detailed.

The tubular portion 23 is provided with an exhaust gas inlet 25 whichopens in to a first exhaust gas chamber 26 and an exhaust gas outlet 27which opens out from a second exhaust gas chamber 28. In use of thecooler 19 in the engine compartment of a road vehicle (not shown), theinlet 25 is connected (directly or by way of an intermediate exhaustconduit (not shown)) to an engine exhaust manifold (not shown) toreceive the hot exhaust gases directly from the vehicle engine (notshown), and the outlet 27 is connected to a pipe (not shown) venting toambient atmosphere (either directly or by way of a silencer (notshown)).

The mutually contiguous first and second exhaust gas chambers 26 and 28are mutually separated within the manifold 21 by means of a baffle plate29 which extends across the manifold 21. The baffle plate 29 issealingly connected to the end wall 41 of the manifold 21 and to a tubeplate 30 (described below).

The exhaust gas inlet 25 and outlet 27 are provided with connectionflanges 42, 43 with threaded holes 44 which are used for theabove-described connections to the inlet 25 and to the outlet 27.However, it is to be understood that other forms of connection may beused.

The opposite ends of the shell 20 are internally sealed by respectivetube plates 30 and 31 whose peripheral shapes correspond to the internalprofile of the shell 20. The volume bounded by the shell 20 and theplates 30, 31 forms a coolant chamber 32 inside the shell 20. Each tubeplate 30 has a number of circular holes 33 arranged through it. Theholes 33 are arranged in a close hexagonal packing (CHP) pattern asshown in FIG. 3, with a gap 34 which corresponds to the position of thebaffle plate 29. The holes 33 in each tube plate 30, 31 are connected bya number of small-diameter tubes 38 which are sealed at one end to thefirst tube plate 30 and at the other end to the second tube plate 31.The gap 34 divides the tubes 38 into a first (upper) sub-set of tubesand a second (lower) sub-set of tubes. The first sub-set of tubes 38extend from the internal outlet from the first (upper) exhaust gaschamber 26, through the first tube plate 30, along the interior of theshell 20 through the coolant chamber 32, and through the second tubeplate 31 into the further exhaust gas chamber 60. The second sub-set oftubes 38 extend from the further exhaust gas chamber 60 through thesecond tube plate 31, along the interior of the shell 20 through thecoolant chamber 32, and through the first tube plate 30 to the internalinlet to the second (lower) exhaust gas chamber 28.

The baffle plate 29 has an aperture 50 in which is positioned abutterfly valve 51 mounted on an axial pin 52. The pin 52 passes throughseatings 53 in the cover 21 and is connected to a control cable (notshown) so that the valve 51 may be controlled remotely to move betweenan open position and a closed position. Although the embodimentillustrated in FIGS. 1-5 employs a butterfly valve 51, it is to beunderstood that the invention can employ any other suitablegas-flow-controlling valve which can be controlled to move between anopen position and a closed position (i.e. between agas-throughflow-permitting position and a gas-throughflow-blockingposition).

FIG. 2 shows (in full lines) the valve 51 in its aperture-closingposition, in which hot exhaust gases from the vehicle engine areprevented from flowing through the aperture 50, and are insteadconstrained to flow in through the exhaust gas inlet 25 into the firstexhaust gas chamber 26, through the bores of the upper sub-set of smalldiameter tubes 38, through the further exhaust gas chamber 60 formed bythe domed cover 24 and the second tube plate 31, back through the boresof the lower sub-set of small diameter tubes 38, through the secondexhaust gas chamber 28 and out of the manifold 20 through the exhaustgas outlet 27.

In the embodiment illustrated in FIGS. 1-3, the tubes 38 may have adiameter of between 5 and 8 mm, preferably about 6.5 mm. The lateralseparation between individual ones of the tubes 38 is preferably about 1mm or less, such that the tube plates 30 & 31 do not present significantobstructions to the flow of exhaust gases. However the invention is notlimited to any particular tube diameter or spacing.

A cooling water inlet pipe 70 is fitted to the shell 20 close to itsfirst end. Similarly, a cooling water outlet 71 pipe is fitted to theshell 20 close to its other end. The inlet and outlet pipes 70, 71 eachcommunicate with the coolant chamber 32 for the supply and draining(respectively) of a coolant fluid (e.g. liquid water). As water (orother coolant fluid) passes from the inlet pipe 70 to the outlet pipe 71and exhaust gases pass along the small diameter tubes 38, heat transfertakes place from the exhaust gas via the surfaces of the small diametertubes 38 to the cooling water in the chamber 32.

When the valve 51 is in its aperture-opening position 51′ (shown indotted outline in FIG. 2), the aperture 50 is unblocked by the valve 50and exhaust gases are permitted to flow from the first exhaust gaschamber 26 directly into the second exhaust gas chamber 28, so bypassingthe tubes 38. Simultaneously, the upper half of the valve 51 blocksexhaust gas flow from the first exhaust gas chamber 26 into the uppersub-set of small diameter tubes 38, and the lower half of the valve 51blocks exhaust gas flow from the lower subset of small diameter tubes 38into the lower exhaust gas chamber 28. Thereby the exhaust gases arediverted from the first exhaust gas chamber 26, through the aperture 50in the baffle plate 29, and directly to the second exhaust gas chamber28, without being cooled by passage through the tubes 38 (from whichexhaust gases are blocked by the valve 51 while in its aperture-openingposition 51′). Hence the cooler 19 provides a simple means of divertingexhaust gases from the cooler when it is not required to cool theexhaust gases, for example on engine start-up.

A mounting plate 45 is provided on one side of the exhaust gas cooler19, to enable the cooler 19 to be secured to a suitable mounting (notshown) within the engine compartment. In the embodiment shown in FIGS.2-5, the mounting plate 45 has three cranked lugs 46 formed by doublebending of the plate 45. The cranking of these lugs 46 serves to spacethe exhaust gas cooler 19 from the surface on which it is mounted. Eachlug 46 is formed with a mounting hole 47 for a bolt or other suitablefastener.

FIG. 6 shows a second embodiment of exhaust gas cooler similar to thatshown in FIGS. 2 to 5 in all essential respects except for thearrangement of the exhaust gas inlet 25, exhaust gas outlet 27, andvalve 151. The same reference signs are therefore used in FIG. 6 toindicate components in the second embodiment which are identical oranalogous to components of the first embodiment 19 of FIGS. 2-5; for adescription of any part of the second embodiment not detailed below,reference should be made to the description of the identical oranalogous component in the first embodiment 19.

In the second embodiment, the baffle plate 29 has an aperture 50 inwhich is positioned a rotatable flap valve 151 mounted on an axial pin152. The pin 152 is connected to a control cable (not shown) so that thevalve 151 may be remotely controlled to rotate between anaperture-closing position and an aperture-opening position as selectedby a vehicle driver or other user. Although the second embodiment asillustrated employs a rotatable flap valve 151, it is to be understoodthat any other suitable valve may alternatively be employed which can beselectively moved between aperture-opening and aperture-closingpositions.

FIG. 6 shows (in full lines) the valve 151 in its aperture-closingposition, in which exhaust gases are constrained to flow from theexhaust gas inlet 25 through the first exhaust gas chamber 26, along thebores of the upper sub-set of small-diameter tubes 38, through thefurther exhaust gas chamber 60 formed by the domed cover 24 and thesecond tube plate 31, back through the bores of the lower sub-set ofsmall-diameter tubes 38, through the second exhaust gas chamber 28 andout through the exhaust gas outlet 27.

In its aperture-closing position, the valve 151 closes off the aperturein the baffle plate 29, so that exhaust gases cannot flow from the firstexhaust gas chamber 26 directly to the second exhaust chamber 28.

When the valve 151 is in its aperture-opening position 151′ as shown indotted outline in FIG. 6, the exhaust gases are no longer constrained topass through the cooling tubes 38, but instead are permitted to flowfrom the first exhaust gas chamber 26 through the aperture and directlyinto the second exhaust gas chamber 28, thus bypassing the cooling tubes38. Furthermore, because the valve 151 positively blocks the passage ofexhaust gas from the exhaust gas inlet 25 to the upper sub-set of tubes38, passage of exhaust gases through the cooling tubes 38 is positivelyblocked. (Instead of the valve 151 being arranged to swing upwards toblock the internal outlet from the first (upper) exhaust gas chamber 26to the upper sub-set of tubes 38 when in its cooler-bypassconfiguration, the valve 151 could alternatively be arranged to swingdownwards to block the internal inlet from the lower sub-set of tubes 38to the second exhaust (lower) gas chamber 28, it being necessary toblock gas flow through the tubes 38 at one end only of these tubes.)

The fact that access is required to only one end of the cooler forconnection of exhaust gas pipes to the inlet and outlet enables theexhaust gas cooler of the invention to fit into spaces in the enginecompartment which could otherwise not be utilised, while maintaining thebenefits of closely packed tubes forming the cooling core. The layout ofthe gas flows in the cooler according to the invention to providetwice-through flow of exhaust gases coupled with a valve-operated bypassfacility is novel while still maximising the efficiency of the gas andcoolant flow. The cooler is highly resistant to corrosion due to itsstainless steel construction, and very robust due to the absence ofsharp corners on the exterior tube.

Although the illustrated embodiments of the invention preferably employa close hexagonal packing arrangement of the internal tubes 38, it is tobe understood that other tube packing arrangements are possible withoutdeparting from the scope of the invention. Although the shell 20 isillustrated as having a transverse cross-section that is generally oval,it is to be understood that other cross-sectional shapes are possiblewithout departing from the scope of the invention; e.g. cross-sectionalshapes which are circular or rectangular.

The manifold 21 and cover 24 which define the various exhaust gaschambers can be formed in various ways. If the manifold 21 is formed asa casting, then the baffle plate 29 may be cast as part of a single-castgas box unit. If the manifold 21 is pressed from sheet, the baffle 29may be attached to the manifold 21 by brazing or welding.

Instead of utilising two tube plates 30, 31 with straight tubes 38extending between the two tube plates, a single tube plate (equivalentto 31) could be employed, with U-shaped tubes extending between holes inthe upper half of the single tube plate to holes in the lower half ofthe same tube plate to carry the exhaust gases through the coolantchamber. As well as halving the number of tube/plate connections, thefurther exhaust chamber 60 could also be eliminated; these advantagesmight outweigh the disadvantage of having to use non-straight tubes.

Other modifications and variations of the invention can be adoptedwithout departing from the scope of the invention as defined in theappended claims.

1. An exhaust gas heat exchanger of the shell and tube type, said heatexchanger comprising a shell having a hollow interior between oppositeends, an exhaust gas manifold secured to one end of the shell, andthermally conductive tube means extending through the interior of theshell from said one end of the shell, the exhaust gas manifoldcomprising first and second exhaust gas chambers which are mutuallyadjacent, each of said exhaust gas chambers comprising a respectiveexhaust gas inlet and an exhaust gas outlet, wherein the exhaust gasinlet of the first exhaust chamber and the exhaust gas outlet of thesecond exhaust chamber are disposed at an angle greater than 0° and lessthan 180°, said tube means providing an exhaust gas flow path betweenthe exhaust gas outlet of said first exhaust gas chamber and the exhaustgas inlet of said second exhaust gas chamber, said heat exchanger beingcharacterised by valve means providing a gas flow path directly betweensaid first and second exhaust gas chambers and substantially closing theexhaust gas outlet of the first exhaust chamber when said valve means isfully open, said valve means substantially closing a direct gas flowpath between said first and second exhaust gas chambers when said valvemeans is closed, whereby when a source of flowing exhaust gas is coupledto the exhaust gas inlet of said first exhaust gas chamber and saidvalve means is closed, exhaust gas is constrained to flow from theexhaust gas inlet of said first exhaust gas chamber to the adjacentexhaust gas outlet of said second exhaust gas chamber by way of saidthermally conductive tube means to exchange heat with fluid in theinterior of the shell and surrounding said tube means, whereas when saidvalve means is open, exhaust gas is allowed to flow from the exhaust gasinlet of said first exhaust gas chamber directly to the adjacent exhaustgas outlet of said second exhaust gas chamber and so bypass said tubemeans.
 2. A heat exchanger as claimed in claim 1 characterised in thatsaid shell is generally tubular between said opposite ends, andcomprises a fluid inlet and a fluid outlet permitting the flow of fluidfrom said fluid inlet to said fluid outlet by way of the interior of theshell surrounding the thermally conductive tube means.
 3. An exhaust gasheat exchanger of the shell and tube type, said heat exchangercomprising a shell having a hollow interior between opposite ends, anexhaust gas manifold secured to one end of the shell, and thermallyconductive tube means extending through the interior of the shell fromsaid one end of the shell, the exhaust gas manifold comprising first andsecond exhaust gas chambers which are mutually adjacent, each of saidexhaust gas chambers comprising a respective exhaust gas inlet and anexhaust gas outlet, said tube means providing an exhaust gas flow pathbetween the exhaust gas outlet of said first exhaust gas chamber and theexhaust gas inlet of said second exhaust gas chamber, said heatexchanger being characterised by valve means providing a gas flow pathdirectly between said first and second exhaust gas chambers when saidvalve means is open, said valve means substantially closing a direct gasflow path between said first and second exhaust gas chambers when saidvalve means is closed, whereby when a source of flowing exhaust gas iscoupled to the exhaust gas inlet of said first exhaust gas chamber andsaid valve means is closed, exhaust gas is constrained to flow from theexhaust gas inlet of said first exhaust gas chamber to the adjacentexhaust gas outlet of said second exhaust gas chamber by way of saidthermally conductive tube means to exchange heat with fluid in theinterior of the shell and surrounding said tube means, whereas when saidvalve means is open, the exhaust gas outlet of said first exhaust gaschamber is substantially closed and exhaust gas is allowed to flow fromthe exhaust gas inlet of said first exhaust gas chamber directly to theadjacent exhaust gas outlet of said second exhaust gas chamber and sobypass said tube means and wherein said thermally conductive tube meanscomprises a plurality of metal tubes extending through said one end ofthe shell, and in that a first sub-set of said plurality of tubesextends from the exhaust gas inlet of said first exhaust gas chamberthrough said other end of the shell and into a further exhaust gaschamber secured to said other end of the shell, and in that a secondsub-set of said tubes extends from said further exhaust gas chamberthrough said other end of the shell to the exhaust gas inlet of saidsecond exhaust gas chamber.
 4. A heat exchanger as claimed in claim 3,characterised in that said further exhaust gas chamber is defined bysaid other end of the shell together with a domed member secured to theshell around said other end of the shell.
 5. A heat exchanger as claimedin claim 1, characterised in that said thermally conductive tube meanscomprises a plurality of metal tubes extending through said one end ofthe shell between the exhaust gas outlet of said first exhaust gaschamber and the exhaust gas inlet of said second exhaust gas chamber. 6.A heat exchanger as claimed in claim 5, characterised in that said tubesare U-shaped.
 7. A heat exchanger as claimed in claim 1, characterisedin that said first and second exhaust gas chambers are mutuallycontiguous on either side of a common internal wall of the manifold,said valve means being mounted in said common internal wall of themanifold.
 8. A heat exchanger as claimed in claim 7, characterised inthat said valve means is a rotary valve mounted for rotation about arotation axis lying substantially in said common internal wall of themanifold.
 9. A heat exchanger as claimed in claim 1, characterised inthat when said valve means is open to allow exhaust gas to flow from theexhaust gas inlet of said first exhaust gas clamber directly to theexhaust gas outlet of said second exhaust gas chamber, the valve meanssubstantially simultaneously closes the exhaust gas inlet of said secondexhaust gas chamber.
 10. A heat exchanger as claimed in claim 1,characterised in that when said valve means is open to allow exhaust gasto flow from the exhaust gas inlet of said first exhaust gas chamberdirectly to the exhaust gas outlet of said second exhaust gas chamber,said valve means substantially directs exhaust gas in the first exhaustchamber at an angle and toward the second exhaust gas chamber.